Device having hinge for treatment of anterior and posterior cruciate ligament injuries and method for using the same

ABSTRACT

A device and method for using the device arranged to maintain anatomical alignment between a joint by creating a dynamic load around the joint to restore and maintain the anatomical alignment. The orthotic device uses a hinge to create a directed force on a tibia by maintaining misalignment of an instant center of rotation (ICoR) of the hinge at a position relative to an anatomical knee joint.

FIELD OF ART

The present disclosure relates generally to the field of orthopedicdevices, and more particularly to an orthotic device having a hinge thatmisaligns the device to create a dynamic load on a body part.

BACKGROUND

An untreated posterior cruciate ligament (PCL) injury heals suboptimally due to laxity caused from lengthening of the PCL. Since laxityof the PCL leads to instability and injury of a person, PCL devices onthe market are used to treat such injuries. These PCL devices generallyuse hinges that have a traditional 4-bar design, a constant forceapplication design, or a constant resistance application design.

The traditional 4-bar design uses a hinge that attempts to closelyimitate the instant center of rotation (ICoR) behavior of the biologicalknee. FIG. 1A illustrates moving ends of the tibia and fibula which cancalculate the ICoR of the biological knee. The traditional 4-bar hingeattempts to closely imitate the movement of the biological knee. As seenin FIG. 1B, the movement of ICoR of the biological knee and traditional4-bar hinge are both relatively stationary, moving only between 10-20mm. This design is used to avoid device migration and/or pistoning ofthe device cuff.

Examples of traditional, prior art braces including traditional 4-barhinges are found in at least: U.S. Pat. No. 4,856,501, granted Aug. 15,1989, U.S. Pat. No. 7,044,925, granted May 16, 2006, and U.S. Pat. No.8,048,013, granted Nov. 1, 2011, and U.S. patent application publication2012/0059296, published Mar. 8, 2012. Each of these documents isincorporated by reference in their entirety.

A constant force design uses a passive, single axis hinge that connectsa femoral cuff to the distal part of the tibial cuff. The proximal endof the tibial cuff can rotate about a pivot point on the distal cuff toallow the pushing of the tibial cuff forward by a spring independent ofthe movement of the hinge. However, as seen in FIG. 2, the forcesexerted by the spring on the proximal tibia are constant regardingflexion angle.

A constant resistance design uses a hinge that provides dampening forcesas the knee flexes, to reduce posterior tibial sag by preventing suddenrotation of the knee. However, to flex the knee joint, the patient mustexert an extra flexion moment by using the hamstring muscle to load theconstant resistance member of the hinge, which causes posterior tibialsag making the device counterproductive.

These known designs, however, are deficient for effectively treating aPCL injury, since these hinges do not prevent the lengthening of the PCLduring flexion of the knee. The traditional 4-bar hinge design is onlyused to track the movement of the biological knee and is not used toprovide a dynamic load to supplement the PCL. The constant force andconstant resistance hinges only provide constant force and may requirethe patient to use muscles for leg movement that may lead to thelengthening of the PCL.

In view of these known designs, there is still a need for an orthopedichinge that provides a dynamic load during flexion and extension of theleg to maintain anatomical alignment of the tibia and fibula to preventthe lengthening of the PCL.

SUMMARY

The present disclosure is directed to a device and method for using thedevice that satisfies the need to maintain anatomical alignment betweena joint by creating a dynamic load around the joint to restore andmaintain the anatomical alignment. An example of this device is anorthotic device that uses a hinge to create an anteriorly directed forceon the tibia by maintaining an ICoR of the hinge at an inferior positionrelative to an anatomical knee joint, when treating a PCL injury.

According to an embodiment, the hinge or pair of hinges are locatedproximate to the knee, and connects upper and lower cuffs. The uppercuff secures to the upper leg, such as over the thigh either theposterior or anterior side, and a lower cuff secures to the lower leg,such as over the shin or calf. Through the ICoR, the lower cuff isarranged and oriented so as to exert the anteriorly directed force fromthe ICoR onto the lower leg to create a desired anatomical correction.

The hinge has an upper linkage with first and second pivoting ends, alower linkage with first and second pivoting ends, and first and secondupright linkages pivotally connected to the first and second pivotingends of the upper and lower linkages. The pivotal connections form anICoR of the hinge located at an inferior position relative to ananatomical knee joint. By maintaining the ICoR of the hinge at aninferior position during flexion and extension of the knee, the hingeattempts to realign a lower tibial cuff of the device, which creates ananteriorly directed force on the tibia. This force generated by therealignment of the device helps unload the PCL at increased flexionangles.

Another example of this device is an orthotic device that uses a hingeto create a posteriorly directed force on the tibia by maintaining anICoR of the hinge at a superior position relative to the anatomical kneejoint. By maintaining the ICoR of the hinge at a superior positionduring flexion and extension of the knee, the device that uses thishinge attempts to realign the lower tibial cuff, but instead, creates aposteriorly directed force on the tibia to effectively unload theanterior cruciate ligament (ACL) at decreased flexion angles.

From the embodiments herein, the linkages of the hinge on the brace aremanipulated to achieve a pattern of movement of an upper or first cuffrelative to a lower or second cuff of the device connected to oneanother by the hinge. The desired relative displacement between theupper and lower cuffs is matched to the hinge, through orientation ofthe linkages of the hinge, which mimics the displacement to generatespecific a load to match the desired anatomical correction or movement;for example shifting of the tibia a minimum of 1 mm, and morespecifically 3 mm anteriorly by the load during flexion of the knee. Thedesired shifting may vary from patient to patient, in that for onepatient the shift may be 3 mm whereas for another patient havingdifferent anatomical proportions the shift may be 5 mm. It is throughthe ICoR that the hinge pushes the cuffs to generate the load for suchanatomical correction.

Methods may be employed to treat injuries of the PCL and ACL using anyof the embodiments of the orthotic devices having the hinges describedabove, in a dynamic manner through extension and flexion of a knee.

The numerous advantages, features and functions of the embodiments willbecome readily apparent and better understood in view of the followingdescription and accompanying drawings. The following description is notintended to limit the scope of the device, hinge and method for usingthe same, but instead merely provides exemplary embodiments for ease ofunderstanding.

BRIEF DESCRIPTION OF THE DRAWINGS

Examples of a device having a hinge designed according to differentembodiments of the present disclosure will now be explained in moredetail referring to the drawings.

FIG. 1A is an illustrative example of the ends of a tibia and fibula tocalculate the theoretical center of rotation for a biological knee.

FIG. 1B is a representative graph of the movement of an ICoR of thebiological knee and a traditional 4-bar hinge.

FIG. 2 shows the force generated by a constant force hinge at differentknee flexion angles.

FIGS. 3A and 3B illustrate two methods for locating an ICoR of a movingbody.

FIGS. 4A and 4B shows a first exemplary embodiment of a device having ahinge having the features of the present disclosure that generates ananteriorly directed force by maintaining an inferior position regardingan anatomical knee joint.

FIGS. 5A-5F are illustrative graph showing the movement of the linkagesof the hinge and ICoR at various degrees of flexion.

FIG. 6 is an illustrative graph showing a shift in the ICoR of the hingehaving the features of the present disclosure relative to a traditional4-bar hinge.

FIG. 7 is an illustrative graph showing a loading of a PCL at differentflexion angles.

FIG. 8 is an illustrative graph showing a dynamic unloading of the PCLby the hinge during a gait cycle of a wearer.

FIG. 9 shows another embodiment of a hinge having the features of thepresent disclosure that generates a posteriorly directed force on thetibia.

FIGS. 10A and 10B show another embodiment of a hinge having the featuresof the present disclosure adjustable for a device in an extended andflexed position.

In the various figures, similar elements are provided with similarreference numbers. The drawing figures are not necessarily drawn toscale, or proportion, but instead are drawn to provide a betterunderstanding of the components, and are not intended to be limiting inscope, but rather provide exemplary illustrations.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS A. Overview

There are approximately 200,000 knee injuries to the ACL, PCL, andcombination of ACL and PCL injuries sustained by people every year. Ofthese injuries, approximately 10% of the knee injuries are to the PCL.

In a healthy knee, the cruciate ligaments, i.e., the PCL and ACL, helpstabilize the knee. The ACL prevents an anterior translation of thetibia regarding the femur, while the PCL helps prevent the posteriortranslation of the tibia regarding the femur. If the ligaments arehealthy, the healthy knee will demonstrate little or no subluxation,i.e., dislocation, from the bending and extending of the knee.

Approximately 50% of ACL injuries are repaired since the ACL is foundwithin a capsule of the knee and cannot heal. A fewer amount of PCLinjuries are surgically repaired, since the PCL is extracapsular andable to spontaneously heal post injury. However, if the PCL may healuntreated, the PCL may heal less optimally.

While there are many other structural elements in the knee, e.g., themeniscus, to help prevent the posterior translation of the tibiaregarding the femur, the majority of force associated with the posteriortranslation of the tibia is absorbed by the PCL. When the PCL isinjured, the PCL can lengthen during the healing process due to straincaused by a posterior shifting of a proximal end of a tibia. Thelengthening of the PCL creates a slack in the healed knee, and mayfurther allow the proximal end of the tibia to continually shiftposteriorly after the healing process which can cause a feeling ofinstability in a patient and increase the risk of injury.

A knee having a PCL deficiency will experience different degrees ofsubluxation, based on the severity of the PCL injury. The severity ofthe PCL laxity/deficiency can be diagnosed using a standard test, i.e.,the posterior drawer test, in which the patient flexes to 90 degreeflexion, and the physician applies a posterior force to the anteriorproximal tibia.

These tests are used to determine the severity of the PCLlaxity/deficiency, which are categorized by a 1 to 3 grading. A grade 1PCL injury is essentially a light sprain, where the fibers of the PCLhave been slightly torn. The grade 1 PCL deficient knee demonstrates aslight posterior subluxation.

A grade 2 PCL injury is a more severe sprain, with the fibers of the PCLare greatly torn, but the PCL is still whole, i.e., the PCL does nothave separated fibers. A grade 3 PCL injury is a full tear of the PCL.Although a grade 3 PCL injury may heal, the PCL will likely becomeexcessively long from the posterior shift of the tibia which may causelaxity in the PCL, as discussed above.

Based on the severity of the PCL injury, the PCL deficient knee willhave varying degrees of subluxation. While a knee having an ACL injuryrequires a posteriorly directed force on the proximal tibia to enhancestabilization and reduce tension on the ACL, a knee having a PCL injuryrequires an anteriorly directed force on a posterior side of theproximal tibia as the knee flexes. By providing support to the posteriorof the proximal tibia at different degrees of flexion, the subluxation,i.e., unwanted shifting can be prevented. By preventing the unwantedshift of the tibia, the lengthening of the PCL during healing may beprevented to offer added stability to the patient and a decreased riskof injury.

In viewing the design of the hinge that supplements the PCL, we firstlook at the rotational motion of a healthy knee. As it is well known,the knee joint is not a single axis joint. The tibia does not rotateabout a single, stationary axis regarding the femur, but instead, thetibia rotates about a moving axis.

The moving axis of the knee joint is called the instant center ofrotation (ICoR), i.e., the center of rotation at any instance such asany flexion angle or time. This movement, e.g., translational androtational movement, of the ICoR is not a wild movement, but rather theICoR only moves within a relatively small circle within the femoralcondyles regarding the tibia and does not travel far from the rotatingbody, i.e., the tibia.

As seen in FIGS. 3A and 3B, there are two methods to find the ICoR of aknee, i.e., the tangent method and the Reuleaux method.

FIG. 3A illustrates that the tangent method considers two points 305,310 on the rotating body 300. As the name implies, the tangents of thesetwo points 305, 310 are found, i.e., the directional vectors of theirmovement 315, 320. Perpendicular lines 325, 330 are then drawn througheach of the points 305, 310 perpendicular to the tangent lines 315, 320respectively. The ICoR of the moving body 300 is determined from thepoint of intersection 335 of the two perpendicular lines 325, 330.

The Reuleaux method uses the same points 305, 310 as used in the tangentmethod but considers the points at two separate instances 306, 311, forexample, at two flexion angles at a first time 305 and a second time306. A line is then drawn between points 305 and 306 and between 310 and311 at the different instances, from which perpendicular lines 340, 345are drawn from the middle of the connecting line. The ICoR of the movingbody 300 is then determined from the point of intersection 350 of thetwo perpendicular lines 340, 345. As the difference in flexion angle ofthe moving body approaches zero, the Reuleaux method converges into thetangent method.

Determining the location of the ICoR is a key element in understandingthe movement of a rotating body and forces that result from the movementduring flexion and extension, since the distance of the ICoR from therotating body determines the relationship between rotational andtranslational movement. When a body moves along a circle with a smallradius, a greater rotational movement will result. Whereas, the bodymoving along a circle having a greater radius will cause greatertranslational movement.

The design of most hinges for orthopedic knee devices attempts toimitate the movement of the ICoR of a healthy knee by incorporating bothrotational and translational movement during flexion and extension ofthe knee, i.e., keeping the ICoR at the same distance from the movingbodies. Incorporating the movement in the hinge axis attempts to createperfect alignment with the anatomical axis of the joint so no movementtakes place between the hinge and the joint, to replicate the naturalmovement.

If the axes are not ideally placed to coincide with the anatomical axisof the joint, during movement of the leg forces will act to relocate thehinge to coincide with the anatomical axis of the knee joint, which willcreate a pressure on the skin or even produce migration issues regardingthe device. The relocation effort of the hinge is generally due tohorizontal misalignment and vertical misalignment of the hinge axis. Inthis discussion, the term “vertical” is defined as a direction along thetibial axis, while the term “horizontal” is defined as a directionperpendicular to the tibial axis in the sagittal plane. It should bekept in mind that the terms vertical and horizontal are relative tocorresponding leg, and not necessarily in a fixed Cartesian space.

Vertical misalignment generally occurs in two ways, i.e., excessivevertical translation and insufficient vertical translation duringflexion and extension. When a hinge has a single axis, there isinsufficient vertical displacement in the device due to the limitedmotion of the ICoR of the hinge axis. This limited motion causes avertical misalignment from the forces acting on the device to seekrealignment of the hinge by moving and end of either the tibial cuff orthe femoral cuff closer to the anatomical axis of the knee joint.

While a hinge having a multi-link system can have excessive verticaldisplacement due to the ICoR of the hinge traveling either too faranteriorly or too far posteriorly regarding the tibial axis during kneeflexion and extension. This displacement creates forces in the hinge toreposition either the tibial cuff or the femoral cuff, which is called“pistoning.” In both cases of vertical displacement, the repositioningof the cuff of the device causes stress at the cuff-skin interface andcan lead to discomfort, skin irritation, and device migration.

Horizontal misalignment can occur due to excessive and insufficienthorizontal translation during movement of the knee joint. Similar to thevertical misalignment in the single axis hinge, insufficient horizontaldisplacement occurs in the single axis hinge when a lack of motion ofthe ICoR causes horizontal misalignment. Excessive horizontaldisplacement can occur in a multilink system when the ICoR of the hingetravels too far superiorly or too far inferiorly along the tibial axisdepending on the anatomical position of the knee.

Horizontal misalignment causes the device to apply pressure to both thetibia and femur. When a device has four points of leverage, all fourpoints are active in applying the load to the body. This load iscompensated by the patient's soft tissue and the soft goods of thedevice as the ICoR of the hinge shifts towards the anatomical axis ofthe knee joint.

In another example to understand the effect of a shifting ICoR of thehinge in relation to a moving body, the tibial cuff of the device isidentified as the moving body, while the femoral cuff is stationary.Three preferred movements are discussed below. In these descriptions,the tibial axis is the axis that runs through the length of the tibia.

The first movement analyzed is the motion created along the tibial axisto generate cuff pistoning. To create this motion along the tibial axis,the ICoR should be positioned far away from the hinge and oriented suchthat the radius of the motion is close to a perpendicular axis to thetibial axis, i.e., the ICoR is located more posterior or more anteriorthan the anatomical knee joint.

The second movement analyzed is the motion to create rotation withminimal translation. This motion to minimize translation is created bylocating the ICoR close to the moving body. By orienting the ICoR insuch a way, translational movement is minimized for each degree ofrotation.

The third movement analyzed is the motion used to create a motionperpendicular to the tibial axis to generate load on the tibia due tomisalignment. This translational movement perpendicular to the tibialaxis, i.e., the sagittal plane, is created by positioning the ICoR faraway from the hinge, and oriented such that the radius of motion isclose to the tibial axis, i.e., the ICoR is located more superiorly ormore inferiorly regarding the tibia depending on the anatomical positionof the knee. Therefore, when the knee is flexed, force can be generatedon the posterior side of the proximal tibia.

B. Discussion of Various Embodiments

As generally discussed above, by understanding the movement of the ICoRof a hinge during different movements of body parts, a device can bedesigned that generates forces to supplement and support an injuredligament during these movements. A knee device can be designed having ahinge that shifts a calf cuff of the device regarding a thigh cuff bycreating forces to realign the device, i.e., creating a “smart”misalignment of the ICoR of the hinge. This “smart” misalignment, or“beneficial” realignment, creates pressure on the tibia at differentranges of motion of the knee by having the ICoR of the hinge positionedeither too far posteriorly or too far anteriorly regarding the tibia tounload an injured PCL or ACL by restoring and maintaining anatomicalalignment of the tibia and fibula.

If the device is aligned too far posteriorly, a posteriorly directedforce is generated at different knee angles on the anterior proximaltibia, and/or an anteriorly directed force is generated on the posteriorof the distal femur. The anterior proximal femur would experience aposteriorly directed force, while the posterior distal tibia wouldexperience an anteriorly directed force. This type of misalignmentresults in the proximal tibia being pushed posteriorly regarding thedistal femur. Although this force would put an additional load on thePCL, the force may be helpful in reducing the load on the ACL.

If the device is aligned too far anteriorly, the direction of the forceson the tibia and femur would be reversed. In this configuration, theposterior proximal tibia and posterior proximal femur would eachexperience an anteriorly directed load, while the anterior distal tibiaand the anterior distal femur would experience a posteriorly directedforce. This would cause the proximal tibia being pushed anteriorlyregarding the distal femur, which would reduce the load on the PCL.

In one embodiment of the present disclosure, an orthotic device having ahinge that creates an increasing dynamic load on the user's tibia isprovided. In this embodiment, it was unexpectedly found that a hingehaving a four-bar hinge design could support an injured PCL bypreventing unwanted shifting of the tibia regarding a femur during thebending and extension of a knee, i.e., throughout various ranges ofmotion of the knee by creating anteriorly directed forces.

The four-bar hinge provides supplemental forces to a tibia of a user bydynamically misaligning a tibial cuff of the device anteriorly when theknee is bent, i.e., at varying degrees of knee flexion, to generate ananteriorly directed force on a posterior of the tibia by maintaining theICoR of the hinge inferiorly regarding the anatomical knee joint. Duringknee flexion and extension, the linkages of the four-bar hinge creates ashift in the calf cuff regarding the thigh cuff creating an anteriorlydirected force to restore and maintain anatomical alignment of the tibiaand fibula.

This configuration of the hinge exploits a joint center at a point offlexion. As the wearer of the device moves his or her knee betweenflexion and extension, the ICoR of the hinge shifts to a positioninferior to the anatomical knee joint axis to create a misalignment ofthe ICoR of the hinge regarding the anatomical knee joint depending onthe angle of flexion. This lack of congruence of these axes creates anopen chain biomechanical force on the anatomical joint as the two axesattempts to coincide with one another. As the flexion angle increases, agreater amount of force will be generated due to the greatermisalignment of the ICoR of the hinge to provide greater support to aninjured PCL.

FIGS. 4A and 4B illustrate an embodiment of the orthotic device havingthe proposed hinge design that maintains the ICoR of the hinge in aninferior position regarding the anatomical knee joint throughout variousknee angles.

For explanatory purposes, the orthotic device may be divided intosections which are denoted by general anatomical terms for the humanbody. Each of these terms is used in reference to a human leg and kneejoint divided in similar sections with a proximal-distal plane (Pr.-D)generally extending along a meniscus of a knee between the femur andtibia. The orthotic device is also divided into anterior and posteriorsections by an anterior-posterior plane (A-Po). The anterior-posteriorplane generally corresponds to the coronal or frontal plane of a humanleg. Each of the anterior and posterior sections may be further dividedabout the center of the knee by a proximal-distal plane and alateral-medial plane. The proximal-distal plane and theanterior-posterior plane generally correspond to an anatomical axis of aknee joint when the orthotic device is worn.

Device 400 is made from a rigid material, such as, plastic, metal,composite fiber, carbon fiber, etc., to provide proper support to theleg of the wearer. The device 400 has an upper femoral cuff 410 andlower tibial cuff 420 connected by hinge 430. The device 400 can alsohave features that are generally well known in the art, for example,padded supports connected to the upper femoral cuff 410 and lower tibialcuff 420 and positioning/tensioning straps connected to the cuffs 410,420 to wrap and position the device 400 around the leg of a wearer. Thepadded supports and straps can be made from materials well known in theart to provide a comfortable and secure attachment of the device 400,e.g., the positioning/tensioning straps can be made from an elastic ornon-elastic fabric and the padded supports can be made from neoprene,foamed polyurethane, or similar support.

Hinge 430 includes two upright linkages 440, 450 connected with upperlinkage 460 and lower linkage 470. The upper linkage 460 and lowerlinkage 470 are connected to the upper femoral cuff 410 and lower tibialcuff 420, respectively, by a connecting element, for example, rivet,screw, button, or similar linking element. The two upright linkages 440,450 are pivotally connected to the upper linkage 460 and lower linkage470 by a similar pivotable linking element to allow the re-positioningof the ICoR of the hinge by the folding of the upright linkages 440,450. The hinge 430 and linkages can be made from a rigid metal, hardplastic or similar material that allows transferring force generated bythe repositioning of the ICoR of the hinge to the lower tibial cuff 420without bending, breaking, or similar failure.

For example, as seen in FIG. 4A, when the device 400 in a fully extendedor extension position, i.e., at a 0 degree flexion angle, the ICoR ofthe hinge 430, i.e., the intersection of the two upright linkages 440and 450, is in a proximal position regarding the anatomical axis of theknee joint. In this state, the ICoR of the hinge 430 is alignedregarding the anatomical knee joint creating an anteriorly directedforce F_(A) to shift the tibial cuff 420 regarding the upper femoralcuff 410 to maintain proper alignment of the tibia and fibula. At theselow angles, however, the hinge generates a lower amount of force thangenerated by a hinge at a higher angle of knee flexion, since theinjured PCL needs little support near full extension.

For example, there may be an anterior shifting of the tibia at a minimumof 1 mm by the load applied by the lower cuff during flexion of theknee. The desired shifting may vary from patient to patient, in that forone patient the shift may be 3 mm whereas for another patient havingdifferent anatomical proportions the shift may be 5 mm. The orientationand placement of the linkages are arranged accordingly.

As schematically exemplified in a simplified manner in FIG. 4B, therelative shift X of the upper cuff to the lower cuff is from an axis A-A(such as, but not specifically, an axis generally defined along theanterior-posterior plane (A-Po) in FIG. 4A) to when the device is inextension to an axis A₁-A₁ when the device is in flexion with the lowercuff shifting relative to the axis A-A. The axis A-A may be treated tocorrespond to both the upper and lower cuffs as they articulate,respectively, and the shift from axis A-A is represented as being fromwhat the lower cuff would have been but for the orientation andplacement of the linkages to cause the displacement of the lower cuffrelative to the upper cuff.

When the knee is flexed in flexion (full flexion being at least 90degrees), as shown in FIG. 4B, the intersection between the two uprightlinkages 440 and 450, shifts the ICoR of the hinge inferiorly away fromthe anatomical axis of the knee joint, which generates anteriorlydirected forces F_(A) on the tibial cuff 420 to shift the lower tibialcuff regarding the upper femoral cuff. As the knee angle increases, agreater amount of force is generated by the greater misalignment of theICoR of the hinge away from the anatomical motion of the knee. Theshift, therefore, generates a greater anteriorly directed force on theposterior of the proximal tibia to provide added posterior support tothe tibia to align the proximal tibia anteriorly than the anteriorlydirected force generated at a lower flexion angle, as discussed above.

The ICoR of the hinge determines the motion of the lower linkage 470 onthe lower tibial cuff regarding the upper linkage 460 on the upperfemoral cuff. By deviating the motion of the lower linkage 470 regardingthe upper linkage 460 from the anatomical motion, a misalignment iscreated between the device and the leg. The misalignment is such that asthe knee angle increases, the lower linkage 470 moves further anteriorlythan expected from the anatomical motion to cause an anteriorly directedforce on the calf.

As seen in the following paragraphs, it was unexpectedly found thatusing a hinge that has a shifting ICoR with respect to regarding theanatomical knee joint could generate similar forces created by a healthyPCL based on the distance of the ICoR of the hinge from the anatomicalknee joint.

The ICoR of the hinge has a shifting ICoR curve starting in a positionadjacent to the anatomical axis of a knee joint and move farther away,i.e., typically in a range of about 10 to about 15 cm, from the hinge toa inferior position with respect to regarding the anatomical knee jointwhen the device moves from a 0 degree flexion angle (extension) to abouta 90 degree flexion angle.

The greater traveling distance of the ICoR of the hinge, as presented inthis disclosure, generates a greater anteriorly directed force on theposterior side of the proximal tibia at various flexion angles due tothis greater inferior movement of the ICoR of the hinge than thetraditional 4-bar hinge. By aligning the hinge at the level of theanatomical axis at full extension and using the mismatch between theanatomical ICoR and the hinge ICoR described above to misalign the hingeas the hinge and knee joint flex, the hinge axis moves to a positionposterior to the anatomical knee axis generating a force to moveanteriorly to locate itself over the anatomical axis. This greatergeneration of force is exploited through the linkages of the hinge tocreate stabilizing biomechanical forces at various flexion angles of theknee; effectively unloading an injured PCL.

The geometry of the ICoR of the hinge 430 is further illustrated inFIGS. 5A-5F. As seen in these figures, the ICoR of the hinge moves toshift the linkages of the hinge 430 at different flexion angles. FIG. 6illustrates the shift data taken and plotted at the flexion angles todetermine the shift generated by the movement of the linkages. Shiftcurve 705 of the hinge having the proposed design has a greater amountof shift than the shift curve of a traditional 4-bar hinge seen in shiftcurve 710. By positioning the ICoR of the hinge inferiorly regarding theanatomical axis, forces are generated on the anterior thigh while theICoR of the hinge shifts inferiorly to create an increased load on theposterior of the tibia.

The shifting of the ICoR of the hinge at various flexion anglesmaintains the shape of the movement of the curve since the knee jointitself also has a moving center of rotation as compared to a traditional4-bar hinge design. The misalignment of the hinge is achieved usingdifferent geometries of the hinge based on the shape of the ICoR curve.Regardless of the geometry of the hinge, however, the force on the tibiais generated from the inferior movement of the ICoR of the hinge basedon the shape of the ICoR curve. To properly generate this force, theICoR of the curve should start proximally to the joint center, moveinferiorly to create the shift of the ICoR, and then return towards thejoint center so as not to increase the misalignment beyond about a 90degree flexion angle. Alternatively, one having ordinary skill in theart appreciates that the ICoR curve of a hinge does not have to returntowards the joint center, so an increasing force is generated beyond a90 degree flexion angle, depending on the injury to be treated.

As illustrated in FIG. 7, the variable loading of the healthy PCL isseen throughout various ranges of motion of the knee. As seen in thepassive knee flexion curve 805, the PCL does not generate a considerableamount of force around the knee during different flexion angles. Agreater amount of force, however, is generated by the PCL on the tibiawith a 100 Newton loaded force on a posterior side of the tibia, whichis illustrated by the 100 N posterior tibial force curve 810. Forexample, at 0-20 degree flexion of the knee, the PCL is not loaded, butas the flexion angle increases, the force on the PCL loads. The loadingof the PCL gradually increases as the knee flexes and reaches a maximumforce at about 100 degree flexion angle. It is understood, that ahealthy PCL provides a posteriorly directed force by pulling on theposterior of the proximal femur or provides an anteriorly directed forceby pulling the posterior of the proximal tibia, mostly during flexion ofthe knee.

When comparing the shift curve 705 of FIGS. 5A-5F, 6 with the loadingcurve 810 in FIG. 7, it was unexpectedly found that the shape of theshift curve was almost identical to the loading curve by the healthy PCLon the tibia. The shape of the misalignment is almost identical to theforces in the PCL throughout the range of motion.

Therefore, the hinge having the ICoR that shifts inferiorly regardingthe anatomical knee joint causes a displacement of the lower tibial cuffwith respect to regarding the upper femoral cuff to provide ananteriorly directed force on the proximal posterior tibia when the kneeis bent to effectively replicate the energy loading of the healthy PCL.The device having this hinge unloads the wearer's PCL by shifting thecalf cuff regarding the thigh cuff to provide proper support andstability for the injured PCL by restoring and maintaining anatomicalalignment of the tibia and fibula.

To get a shift curve that resembles the loading curve of the PCL as seenin FIG. 8, the ICoR of the hinge must be located proximally for thefirst 20 degrees of flexion. When the hinge flexes beyond 20 degrees,the ICoR of the hinge moves inferiorly, to create horizontalmisalignment so the tibial cuff is located more anteriorly than thetibia.

When the device 400 has an increased flexion angle, the hinge 430generates a greater force on a posterior side of the proximal tibia byshifting the ICoR of hinge inferiorly regarding the anatomical motion ofthe knee joint. As the knee continues to flex, the ICoR of the hingemoves further inferiorly to create a greater misalignment with respectto regarding the anatomical knee joint. When the knee reaches about a 90degree flexion angle, the ICoR returns to a more proximal position tomaintain the misalignment of the ICoR regarding the anatomical axis ofthe knee joint and does not increase as the knee flexes beyond 90degrees.

FIG. 8 further provides evidence of the unexpected load created bymisaligning the ICoR of the hinge with respect to regarding theanatomical axis of the knee joint. As shown in FIG. 8, when the devicehaving the hinge, is worn by a user on the right leg, a greater dynamicunloading of the PCL is provided during a gait cycle. As the userprovides a greater flexion angle during the gait cycle, a greater amountof unloading is provided, as seen in unloading curve 905, by the hingedue to the increased shift of the ICoR of the hinge from the anatomicalknee joint.

The different embodiments of the hinge discussed above use themisalignment of the ICoR of the hinge to generate forces on the proximalposterior tibia and the distal anterior femur to prevent posteriorsubluxation of the tibia, i.e., restore and/or maintain anatomicalalignment of the tibia and the fibula. This would then effectivelysupplement the action of a healthy PCL by having the device providevarying loads to the tibia to mirror the loading behavior of the healthyPCL. This added support may prevent a lengthening of the PCL during thehealing process and prevent shifting problems to give a wearer an addedfeeling of stability and a decreased risk of injury.

One having ordinary skill in the art can appreciate that the positioningof the ICoR of the hinge regarding the anatomical axis can be altered totreat different knee injuries or provide different supporting forces ona knee by a device using the hinge. For example, as discussed above, theAs ICoR of the hinge can move superiorly with respect to regarding theanatomical axis of the knee joint to treat a knee having an ACL injury.In this case, the positioning of the ICoR of the hinge is used to createa posteriorly directed force on the proximal anterior tibia tosupplement an injured ACL during knee extension.

FIG. 9 shows device 1000 having hinge 1030 that creates a greaterposteriorly directed force F_(P) near full extension, i.e., zero degreeflexion, than at ninety degree flexion. Hinge 1030 is constructedsimilarly to hinge 430 and is pivotally connected to upright linkages1040, 1050, and connects the upper femoral cuff 1010 to the lower tibialcuff 1020. Hinge 1030, however, has an ICoR that moves furthersuperiorly with respect to regarding the anatomical knee joint as theknee reaches full extension to provide greater support to an injuredACL. The force generated by the movement of the ICoR causes a shift ofthe lower tibial cuff 1020 posteriorly during extension. This creates anincreasing dynamic load in front of the tibia which effectively unloadsthe ACL, protecting it from undue tension.

An adjustable hinge can be designed that can create either a posteriorlyor anteriorly directed force on the device by allowing there-positioning of the ICoR of the hinge. By allowing such an adjustmentof the linkages, the directed forces can selectively treat an injury sothat during flexion and extension movements of the knee the anatomicalalignment of the tibia and fibula can be restored and maintained.

As seen in FIGS. 10A and 10B, an adjustable 4-bar linkage hinge providesan anteriorly directed force on a posterior side of a proximal tibia.Hinge 1100 has an upper femoral connection linkage 1105 and lower tibialconnection linkage 1110. The upper femoral connection linkage 1105 hasone end connected to an upper linkage 1115, while the other end isconnected to a femoral cuff of a device (not shown). The lower tibialconnection linkage 1110 has one end connected to a lower linkage 1120and the other end connected to a tibial cuff of the device of any typeshown and known in the prior art. A first upright linkage 1125 ispivotally connected to the upper linkage 1115 and lower linkage 1120 ona first side of the hinge 1100. A second upright linkage 1130 is thenconnected to the upper linkage 1115 and lower linkage 1120 on a secondside of hinge 1100.

As shown in FIG. 10B, by having this configuration, the hinge 1100 cancollapse from a first position having a polygonal shape to a secondposition where a corner formed from the intersection of the upperlinkage 1115 and first upright linkage 1125 shifts to fold behind thelower linkage 1120 and second upright linkage 1130. By having the pivotpoints on the linkages 1125 and 1130 adjustable on the upper linkage1115 and lower linkage 1120, the ICoR of the hinge can be adjusted totreat various knee injuries.

The adjustment of the hinge 1100 can be accomplished by using anadjustable screw and nut 1135 that connects the first upright linkage1125 in groove 1140 in different lateral and vertical positions relativeto upper linkage 1115. Similarly, the second upright linkage 1130 has ascrew and nut 1145 that allows the adjustment of the second uprightlinkage 1130 regarding the lower linkage 1120 within groove 1150. Theupper linkage 1115 also has a screw and nut 1155 that allows theadjustment of the second upright linkage with respect to regarding theupper linkage 1115 within groove 1160.

One having ordinary skill in the art would appreciate that theadjustment of the linkages is not limited to a screw and nut adjustablewithin a groove, but the adjustment can be accomplished by other wellknown means in the art. A slidable pin can position the linkages indifferent positions by being slid into slots along the linkages.

While the foregoing embodiments have been described and shown,alternatives and modifications of these embodiments, such as thosesuggested by others, may be made to fall within the scope of thedisclosure. Any of the principles described may be extended to any otherorthopedic devices or other types of articles requiring similarfunctions of those structural elements described.

The invention claimed is:
 1. An orthotic device having a first andsecond cuffs connected to one another by an articulating hinge betweenfirst and second positions, the orthotic device defining aproximal-distal plane, and an anterior-posterior plane intersecting oneanother to form an intersection axis, the hinge comprising: a firstlinkage system having a first end connecting to the first cuff and asecond end; a second linkage system having a first end connecting to thesecond cuff and a second end pivotally connecting to the second end ofthe first linkage, the pivotal connection of the first and secondlinkage systems forming an instant center of rotation (ICoR) located atan anterior or posterior side relative to the anterior-posterior plane,and urging a force directed through the second cuff due to a relativedisplacement of the first cuff relative to the second cuff whichincreases as the orthotic device approaches full flexion; wherein theICoR of the hinge shifts to a position relative to the anatomical kneejoint axis to create a misalignment of the ICoR depending on the angleof flexion.
 2. The orthotic device according to claim 1, wherein thefirst and second linkage systems are pivotally connected by a linkingelement selected from the group consisting of rivet, bolt, screw, orbutton.
 3. The orthotic device according to claim 1, wherein the ICoR ismaintained at the position which is arranged inferiorly relative to theanatomical knee joint during flexion and extension.
 4. The orthoticdevice according to claim 1, wherein the first linkage system includes afirst linkage having first and second pivoting ends and a first uprightlinkage, and the second linkage system includes a second linkage havingfirst and second pivoting ends and a second upright linkage, the firstand second upright linkages pivotally connected to the first and secondpivoting ends of the first and second linkages, the pivotal connectionof the first and second upright linkages forming an instant center ofrotation (ICoR) of the hinge located at a superior or inferior positionrelative to the intersection axis.
 5. The orthotic device according toclaim 4, wherein the first upright linkage is pivotally connected to thefirst pivoting end of the first linkage and the second pivoting end ofthe second linkage and the second upright linkage is pivotally connectedto the second pivoting end of the first linkage and the first pivotingend of the second linkage.
 6. The orthotic device according to claim 1,wherein the ICoR of the hinge shifts a greater distance at a greaterflexion angle during flexion of an anatomical knee joint.
 7. Theorthotic device according to claim 4, wherein the pivotal connectionbetween the first linkage and the first upright linkage and the secondupright linkage is adjustable.
 8. The orthotic device according to claim4, wherein the pivotal connection between the second linkage and thefirst upright linkage and the second upright linkage is adjustable. 9.The orthotic device according to claim 4, wherein in extension, thefirst linkage is generally located on the proximal side of theproximal-distal plane.
 10. The orthotic device according to claim 4,wherein in extension, the first linkage folds over the second linkage.11. The orthotic device according to claim 4, wherein in flexion, thesecond linkage moves anteriorly to form an anteriorly directed force.12. The orthotic device according to claim 1, wherein in extension, thehinge is misaligned in regard to the intersection axis.
 13. The orthoticdevice according to claim 1, wherein second cuff shifts relative to thefirst cuff in either a posteriorly or anteriorly direction at least 1 mmfrom an axis along which the first and second cuffs extend in the secondposition, relative to when the first and second cuffs extend in a firstposition.
 14. The orthotic device according to claim 1, wherein thefirst cuff is a femoral cuff and the second cuff is a tibial cuff. 15.An orthotic device having a first cuff and a second cuff connected toone another by an articulating hinge between first and second positions,the orthotic device defining a proximal-distal plane, and ananterior-posterior plane intersecting one another to form anintersection axis, the hinge comprising: a first linkage system havingfirst and second pivoting ends; a second linkage system having first andsecond pivoting ends; and the pivotal connection of the first and secondlinkage systems forming an instant center of rotation (ICoR) of thehinge located at a position relative to the intersection axis, andtransmitting either an anteriorly or posteriorly directed force throughthe second cuff due to a relative displacement of the first cuffrelative to the second cuff thereby increasing or decreasing as thehinge articulates; wherein second cuff shifts relative to the first cuffin either a posteriorly or anteriorly direction at least 1 mm from anaxis along which the first and second cuffs extend in the secondposition, relative to when the first and second cuffs extend in a firstposition.
 16. The orthotic device according to claim 15, wherein thefirst linkage system includes a first linkage having first and secondpivoting ends and a first upright linkage, and the second linkage systemincludes a second linkage having first and second pivoting ends and asecond upright linkage, the first and second upright linkages pivotallyconnected to the first and second pivoting ends of the first and secondlinkages, the pivotal connection of the first and second uprightlinkages forming an instant center of rotation (ICoR) of the hingelocated at a superior or inferior position relative to the intersectionaxis.
 17. The orthotic device according to claim 16, wherein the firstupright linkage is pivotally connected to the first pivoting end of thefirst linkage and the second pivoting end of the second linkage and thesecond upright linkage is pivotally connected to the second.
 18. Theorthotic device according to claim 16, wherein the ICoR is maintained atthe position which is arranged superiorly or inferiorly relative to theanatomical knee joint during flexion and extension.
 19. A method forusing an orthotic device on a leg, the orthotic device having a firstcuff, a second cuff, and a hinge comprising first and second linkagesystems, where the pivotal connection forms an instant center ofrotation (ICoR) located at a first position relative to an anatomicalknee joint, the method of using the orthotic device comprising the stepsof: flexing the anatomical knee joint; shifting the ICoR of the hinge tomove to a second position further from the first position relative to ananterior-posterior plane with respect to the anatomical knee joint atgreater flexion angles; and transmitting either an anteriorly orposteriorly directed force through the second cuff due to a relativedisplacement of the first cuff relative to the second cuff therebyincreasing or decreasing as the hinge articulates.
 20. The methodaccording to claim 19, wherein the second cuff shifts relative to thefirst cuff in either a posteriorly or anteriorly direction at least 1 mmfrom an axis along which the first and second cuffs extend in the secondposition, relative to when the first and second cuffs extend in a firstposition.